Previously, when I wanted to move/copy a message from one folder to another I right clicked on the message title in the list and from the pop-up menu selected Move/Copy and its arrowhead which then expanded to show my available folders. Now, in Thunderbird 45, running on a Windows PC, the pop-up menu appears ok but it does not expand to show the folders. Instead, a tiny empty square appears at the edge of the menu frame, at the Move/Copy line (the same happens if I use the menu bar Message item). Hitting that square with either mouse button has no effect. Is there some setting I haven't noticed or too many folders (though I haven't added any lately) or what? Dragging and dropping works fine but I'd like to use menus.